Naphthoxazine benzoxazine-based monomer, polymer thereof, electrode for fuel cell including the polymer, electrolyte membrane for fuel cell including the polymer, and fuel cell using the electrode

ABSTRACT

A naphthoxazine benzoxazine-based monomer is represented by Formula 1 below: 
     
       
         
         
             
             
         
       
         
         In Formula 1, R 2  and R 3  or R 3  and R 4  are linked to each other to form a group represented by Formula 2 below, and R 5  and R 6  or R 6  and R 7  are linked to each other to form a group represented by Formula 2 below, 
       
    
     
       
         
         
             
             
         
       
         
         In Formula 2, * represents the bonding position of R 2  and R 3 , R 3  and R 4 , R 5  and R 6 , or R 6  and R 7  of Formula 1. A polymer is formed by polymerizing the naphthoxazine benzoxazine-based monomer, an electrode for a fuel cell includes the polymer, an electrolyte membrane for a fuel cell includes the polymer, and a fuel cell uses the electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application of U.S. application Ser. No.12/262,854, filed Oct. 31, 2008, now U.S. Pat. No. 8,188,210, issued May29, 2012, which claims the benefit of Korean Patent Application No.10-2007-0111587, filed on Nov. 2, 2007 and Korean Patent Application No.10-2008-0099351, filed on Oct. 9, 2008, in the Korean IntellectualProperty Office, the disclosures of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

One or more embodiments of the present invention relate to anaphthoxazine benzoxazine-based monomer, a polymer thereof, an electrodefor a fuel cell including the polymer, an electrolyte membrane for afuel cell including the polymer, and a fuel cell using the electrode.

2. Description of the Related Art

Fuel cells, which use a polymer electrolyte membrane as an electrolyte,operate at a relatively low temperature and can be small in size. Thus,fuel cells may be used as power sources in electric vehicles ordistributed generation systems for homes. As a polymer electrolytemembrane used in polymer electrolyte fuel cells, aperfluorocarbonsulfonic acid-based polymer membrane such as NAFION(registered trademark) has been used.

However, such polymer electrolyte membranes typically need water toprovide proton conduction abilities, and thus the polymer electrolytemembranes typically need to be humidified. In addition, to enhance cellsystem efficiencies, it may be necessary to operate polymer electrolytemembranes at a high temperature of at least 100° C. However, themoisture in polymer electrolyte membranes may evaporate at thistemperature, and the polymer electrolyte membranes may not functionproperly as a solid electrolyte.

To address those problems in the art, non-humidified electrolytemembranes that can operate at a high temperature of at least 100° C.under nonhumidified conditions have been developed. For example, U.S.Pat. No. 5,525,436 discloses polybenzimidazole doped with a phosphoricacid, and the like as a material constituting non-humidified electrolytemembranes.

In addition, in cells that operate at a low temperature, such as cellsusing a perfluorocarbonsulfonic acid-based polymer membrane, to preventgas diffusion in electrodes due to water (formation water) that isproduced as electricity is generated in an electrode, particularly acathode, electrodes using polytetrafluoroethylene (PTFE) as a waterproofagent to have hydrophobic properties have been widely used (see, forexample, Japanese Patent Laid-Open Publication No. hei 05-283082).

In addition, phosphoric acid type fuel cells operating at a hightemperature of 150 to 200° C. use a liquid phosphoric acid as anelectrolyte. However, a large amount of the liquid phosphoric acid ispresent in electrodes, which interferes with gas diffusion. Therefore,an electrode catalyst layer that is formed by addingpolytetrafluoroethylene (PTFE) as a waterproof agent to an electrodecatalyst, and which can prevent fine pores in electrodes from beingclogged by a phosphoric acid, has been used.

In addition, in fuel cells using a polybenzimidazole (PBI) electrolytemembrane, which retains phosphoric acid as a nonhumidified electrolyteat a high temperature, to reduce contact between electrodes and theelectrolyte membrane, a method of impregnating electrodes with a liquidphosphoric acid has been tried and a method of increasing a loadingamount of metal catalysts has been tried. However, such fuel cells havenot exhibited improved properties, and thus there is a need forimprovement.

In addition, when air is supplied to a cathode when a solid polymerelectrolyte doped with phosphoric acid is used, the fuel cell requiresan aging time of about 1 week even if the composition of the cathode isoptimized. By supplying oxygen to the cathode instead of air,performance of the cathode can be improved and aging time can also bereduced. However, the need to supply of oxygen to the cathode is anobstacle in realizing widespread use of the cathode.

SUMMARY OF THE INVENTION

One or more embodiments of the present invention include a naphthoxazinebenzoxazine-based monomer, a polymer thereof, an electrode for a fuelcell including the polymer, an electrolyte membrane for a fuel cellincluding the polymer, and a fuel cell which includes an electrode for afuel cell formed using the polymer thereof, thereby having improved cellperformance.

Additional aspects and/or advantages will be set forth in part in thedescription which follows and, in part, will be apparent from thedescription, or may be learned by practice of the invention.

According to an embodiment of the present invention, there is provided anaphthoxazine benzoxazine-based monomer represented by Formula 1 below:

wherein R₂ and R₃ or R₃ and R₄ are linked to each other to form a grouprepresented by Formula 2 below, and

R₅ and R₆ or R₆ and R₇ are linked to each other to form a grouprepresented by Formula 2 below,

wherein, in Formula 2, R₁ is a substituted or unsubstituted C₁-C₂₀ alkylgroup, a substituted or unsubstituted C₁-C₂₀ alkoxy group, a substitutedor unsubstituted C₂-C₂₀ alkenyl group, a substituted or unsubstitutedC₂-C₂₀ alkynyl group, a substituted or unsubstituted C₆-C₂₀ aryl group,a substituted or unsubstituted C₆-C₂₀ aryloxy group, a substituted orunsubstituted C₇-C₂₀ arylalkyl group, a substituted or unsubstitutedC₂-C₂₀ heteroaryl group, a substituted or unsubstituted C₂-C₂₀heteroaryloxy group, a substituted or unsubstituted C₂-C₂₀heteroarylalkyl group, a substituted or unsubstituted C₄-C₂₀ carbocyclegroup, a substituted or unsubstituted C₄-C₂₀ carbocyclic alkyl group, asubstituted or unsubstituted C₂-C₂₀ heterocycle group, or a substitutedor unsubstituted C₂-C₂₀ heterocyclic alkyl group,

in Formula 2, * represents the bonding position of R₂ and R₃, R₃ and R₄,R₅ and R₆, or R₆ and R₇ of Formula 1, and

R₂ or R₄ that does not form a group of Formula 2 is hydrogen and R₅ orR₇ that does not form a group of Formula 2 is hydrogen.

According to an embodiment of the present invention, there is provided apolymer of a naphthoxazine benzoxazine-based monomer which is apolymerization product of the naphthoxazine benzoxazine-based monomerdescribed above or a polymerization product of the naphthoxazinebenzoxazine-based monomer described above and a crosslinkable compound.

According to an embodiment of the present invention, there is providedan electrode for a fuel cell, the electrode comprising a catalyst layercomprising the polymer of the naphthoxazine benzoxazine-based monomer.

According to an embodiment of the present invention, there is providedan electrolyte membrane for a fuel cell, the electrolyte membranecomprising the polymer of the naphthoxazine benzoxazine-based monomer.

According to an embodiment of the present invention, there is provided afuel cell comprising a cathode; an anode; and an electrolyte membraneinterposed between the cathode and the anode, wherein at least one ofthe cathode and the anode comprises a catalyst layer comprising thepolymer of the naphthoxazine benzoxazine-based monomer described aboveor wherein the electrolyte membrane comprises the polymer of thenaphthoxazine benzoxazine-based monomer described above.

Additional aspects and/or advantages of the invention will be set forthin part in the description which follows and, in part, will be obviousfrom the description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages will become apparent and morereadily appreciated from the following description of the embodiments,taken in conjunction with the accompanying drawings of which:

FIG. 1 is a graph showing thermogravimetric analysis (TGA) results of acompound prepared in Synthesis Example 1, a compound prepared inSynthesis Example 4, and t-BuPh-a prepared in Reference Example 1;

FIG. 2 is a graph showing a change in voltage with respect to time offuel cells prepared in Example 1 and Comparative Example 1;

FIG. 3 is a graph showing a change in cell potential with respect tocurrent density of fuel cells prepared in Examples 1 and 2 andComparative Example 1;

FIGS. 4 through 9 are graphs showing nuclear magnetic resonance (NMR)spectra of target materials prepared in Synthesis Examples 1 through 5,respectively;

FIGS. 10 and 11 are graphs showing TGA results of 16DHN3AP and27DHN34DFA and TGA results of a polymer of 16DHN3AP and PBI and apolymer of 27DHN34DFA and PBI prepared in Synthesis Examples 7 and 8,respectively;

FIG. 12 is a graph showing voltage characteristics according to currentdensity of a fuel cell prepared in Example 6;

FIG. 13 is a graph showing a change in cell voltage according to time ofa fuel cell prepared in Example 6;

FIGS. 14 and 15 are graphs respectively showing conductivity accordingto temperature and phosphoric acid doping level of electrolyte membranesprepared in Examples 6 through 9;

FIG. 16 is a graph showing a solid NMR spectrum of a polymer of27DHN34DFA and PBI according to an embodiment of the present invention;and

FIG. 17 is a graph showing cell voltage characteristics according tocurrent density of fuel cells prepared in Example 10 and ComparativeExample 2.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the present embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to the like elementsthroughout. The embodiments are described below in order to explain thepresent invention by referring to the figures.

A naphthoxazine benzoxazine-based monomer according to an embodiment ofthe present invention is represented by Formula 1 below:

wherein R₂ and R₃ or R₃ and R₄ are linked to each other to form a grouprepresented by Formula 2 below, and

R₅ and R₆ or R₆ and R₇ are linked to each other to form a grouprepresented by Formula 2 below.

In Formula 2, R₁ is a substituted or unsubstituted C₁-C₂₀ alkyl group, asubstituted or unsubstituted C₁-C₂₀ alkoxy group, a substituted orunsubstituted C₂-C₂₀ alkenyl group, a substituted or unsubstitutedC₂-C₂₀ alkynyl group, a substituted or unsubstituted C₆-C₂₀ aryl group,a substituted or unsubstituted C₆-C₂₀ aryloxy group, a substituted orunsubstituted C₇-C₂₀ arylalkyl group, a substituted or unsubstitutedC₂-C₂₀ heteroaryl group, a substituted or unsubstituted C₂-C₂₀heteroaryloxy group, a substituted or unsubstituted C₂-C₂₀heteroarylalkyl group, a substituted or unsubstituted C₄-C₂₀ carbocyclicgroup, a substituted or unsubstituted C₄-C₂₀ carbocyclic alkyl group, asubstituted or unsubstituted C₂-C₂₀ heterocyclic group, or a substitutedor unsubstituted C₂-C₂₀ heterocyclic alkyl group,

in Formula 2, * represents the bonding position of R₂ and R₃, R₃ and R₄,R₅ and R₆, or R₆ and R₇, respectively, of Formula 1, and

R₂ or R₄ that does not form a group of Formula 2 is hydrogen and R₅ orR₇ that does not form a group of Formula 2 is hydrogen.

As non-limiting examples, R₁ may be one selected from groups representedby the following formulae.

As non-limiting examples, the naphthoxazine benzoxazine-based monomermay be at least one selected from compounds represented by Formulae 3through 5.

In Formulae 3 through 5, R₁ may be a group as defined in Formula 1, and,as non-limiting examples, may be selected from groups represented by thefollowing formulae.

The naphthoxazine benzoxazine-based monomer according to aspects of thepresent invention has structural stiffness due to an increase incrosslinked sites. In addition, when the naphthoxazine benzoxazine-basedmonomer is used in forming an electrode for a fuel cell, fluorine, afluorine-containing functional group, or a pyridine functional group isintroduced into the monomer as described above, and thus oxygentransmittance and an amount of phosphoric acid injected into theelectrode can be increased and thermal resistance and resistance tophosphoric acid can be obtained at the same time.

In addition, the naphthoxazine benzoxazine-based monomer according to anembodiment of the present invention includes a naphthoxazine group thatcan maximize a hydrogen bond in a molecule and a hydrogen bond betweenmolecules, and thus, when the naphthoxazine benzoxazine-based monomer isco-polymerized with a crosslinkable compound, the number ofcrosslinkable sites increases. Thus, by using the naphthoxazinebenzoxazine-based monomer, a fuel cell that can have excellent thermalstability and durability at an operating temperature, and thereby havinga long lifetime, can be prepared.

In addition, when the naphthoxazine benzoxazine-based monomer issimultaneously used in an electrode and an electrolyte membrane, thecompatibility of an interface between the electrolyte membrane and theelectrode is enhanced. Thus, the performance of a fuel cell can bemaximized.

The naphthoxazine benzoxazine-based monomer represented by Formula 1 maybe one selected from compounds represented by Formulae 6 through 11.

Hereinafter, a method of preparing the naphthoxazine benzoxazine-basedmonomer of Formula 1 according to aspects of the present invention willbe described. As an embodiment of the present invention, a method ofpreparing the compounds represented by Formulae 3 through 5 will now bedescribed; however, the other compounds described above can besynthesized in a manner similar to the preparation method describedherein.

Referring to Reaction Scheme 1 below, the compound of Formula 3 can beprepared by heating 1,5-dihydroxynaphthalene (A), p-formaldehyde (B) andan amine compound (C) without a solvent or by adding a solvent to A, Band C and then refluxing the mixture, and thereafter working up theresultant. Referring to Reaction Schemes 2 and 3, the compound ofFormula 4 and the compound of Formula 5 can be prepared in the samemanner as in Reaction Scheme 1, except that 1,6-dihydroxynaphthalene(A′) or 2,7-dihydroxynaphthalene (A″) are used instead of1,5-dihydroxynaphthalene (A).

In Reaction Schemes 1 through 3, R₁ may be selected from the same groupsrepresented by the following formulae as defined in Formulae 3 through5.

The solvent used in the reactions described above may be 1,4-dioxane,chloroform, dichloromethane, THF, or the like. The heating temperatureis adjusted to a temperature range that can reflux the solvent, such as,for example, a range of 80 to 110° C., or more specifically, about 110°C.

As a non-limited embodiment of the working-up process, the resultantreaction mixture is washed with an aqueous 1N NaOH solution and waterand dried using a drier such as magnesium sulfate, and then theresultant is filtered and evaporated under reduced pressure in order toremove the solvent from the resultant, and dried to obtain a targetmaterial.

Non-limiting examples of the C₁-C₂₀ alkyl group” include methyl, ethyl,propyl, isobutyl, sec-butyl, pentyl, iso-amyl, hexyl, or the like. TheC₁-C₂₀ alkyl group may be unsubstituted, or at least one hydrogen atomof the alkyl group may be substituted with a halogen atom such asfluorine and chlorine, a C₁-C₂₀ alkyl group substituted with a halogenatom (such as, for example, CCF₃, CHCF₂, CH₂F, CCl₃, and the like), ahydroxyl group, a nitro group, a cyano group, an amino group, an amidinogroup, hydrazine, hydrazone, a carboxyl group or a salt thereof, asulfonic acid group or a salt thereof, a phosphoric acid or a saltthereof, a C₁-C₂₀ alkyl group, a C₂-C₂₀ alkenyl group, a C₂-C₂₀ alkynylgroup, a C₁-C₂₀ heteroalkyl group, a C₆-C₂₀ aryl group, a C₅-C₂₀arylalkyl group, a C₆-C₂₀ heteroaryl group, a C₁-C₂₀ heterocyclic group,or a C₆-C₂₀ heteroarylalkyl group.

The term “aryl group” as used herein refers to a C₆-C₂₀ carbocyclicaromatic system containing at least one ring, wherein the rings can bependantly attached to each other or fused with each other. The term“aryl,” as used alone or in combination with other terms, refers to anaromatic radical, such as, for example, phenyl, naphthyl,tetrahydronaphthyl, or the like. The aryl group may be unsubstituted orat least one hydrogen atom of the aryl group may be substituted with asubstituent described above with respect to the alkyl group.

As non-limiting examples, the aryloxy group may be a phenoxy group, anaphthyloxy group, a tetrahydronaphthyloxy group, or the like. Thearyloxy group may be unsubstituted or at least one hydrogen atom of thearyloxy group may be substituted with a substituent described above withrespect to the alkyl group.

The term “heteroaryl group” as used herein refers to a monovalent,monocyclic or bicyclic aromatic bivalent organic compound that contains1, 2 or 3 hetero atoms selected from the group consisting of N, O, P,and S and has 1 to 20 carbon atoms. As non-limiting examples, theheteroaryl group may be pyrazinyl, furanyl, thienyl, pyridyl,pyrimidinyl, isothiazolyl, oxazolyl, thiazolyl, triazolyl,1,2,4-thiadiazolyl, or the like. The heteroaryl group may beunsubstituted or at least one hydrogen atom of the heteroaryl group maybe substituted with a substituent described above with respect to thealkyl group.

As non-limiting examples, the heteroaryloxy group may be pyrazinyloxy,furanyloxy, thienyloxy, pyridyloxy, pyrimidinyloxy, isothiazolyloxy,oxazolyloxy, thiazolyloxy, triazolyloxy, 1,2,4-thiadiazolyloxy, or thelike. The heteroaryloxy group may be unsubstituted or at least onehydrogen atom of the heteroaryloxy group may be substituted with the asubstituent described above with respect to the alkyl group.

The term “heterocyclic group” as used herein refers to a 5 to 10membered group containing a hetero atom such as nitrogen, sulfur,phosphorus, oxygen, and the like. The heterocyclic group may beunsubstituted or at least one hydrogen atom of the heterocycle group maybe substituted with a substituent described above with respect to thealkyl group.

As non-limiting examples, the cycloalkyl group may be a cyclohexylgroup, a cyclopentyl group, or the like. The cycloalkyl group may beunsubstituted or at least one hydrogen atom of the cycloalkyl group maybe substituted with a substituent described above with respect to thealkyl group.

An embodiment of the present invention also provides a polymer of thenaphthoxazine benzoxazine-based monomer of Formula 1.

The polymer can be prepared by dissolving the naphthoxazinebenzoxazine-based monomer of Formula 1 in a solvent, and thenpolymerizing the resultant by a heat treatment, such as, for example, aheat treatment at a temperature range of 180 to 250° C. When the heattreatment temperature is less than 180° C., reactivity of polymerizationmay be degraded. On the other hand, when the heat treatment temperatureis greater than 250° C., an unreacted compound may be produced so thatthe product yield may be reduced.

In this reaction, a polymerization catalyst, and the like can be used,if necessary.

The solvent used in the polymerization reaction may beN-methylpyrrolidone (NMP), dimethylacetamide (DMAc), or the like, andthe amount of the solvent may be in the range of 5 to 30 parts by weightbased on 100 parts by weight of the naphthoxazine benzoxazine-basedmonomer of Formula 1.

An embodiment of the present invention also provides a polymer that is apolymerization product of the naphthoxazine benzoxazine-based monomer ofFormula 1 and a crosslinkable compound.

The crosslinkable compound may be at least one of polybenzimidazole, apolybenzimidazole-base complex, polybenzthiazole, polybenzoxazole andpolyimide.

The amount of the crosslinkable compound may be in the range of 5 to 95parts by weight based on 100 parts by weight of the naphthoxazinebenzoxazine-based monomer of Formula 1.

When the polymer of the naphthoxazine benzoxazine-based monomer ofFormula 1 according to aspects of the present invention is used informing an electrode for a fuel cell, oxygen transmission is improvedeven when only air is supplied to a cathode, and wettability ofphosphoric acid (H₃PO₄) in an electrode and thermal stability can beimproved.

In addition, when the polymer of the naphthoxazine benzoxazine-basedmonomer is used in forming an electrolyte membrane for a fuel cell,thermal stability and durability of the electrolyte membrane at anoperating temperature are improved.

Therefore, a fuel cell employing the electrode and an electrolytemembrane can operate at a high temperature under nonhumidifiedconditions, can have enhanced thermal stability, and can exhibitimproved electricity generation performance.

The electrode for a fuel cell, according to aspects of the presentinvention includes a catalyst layer comprising a polymerization productof the naphthoxazine benzoxazine-based monomer of Formula 1 or a polymerof the naphthoxazine benzoxazine-based monomer of Formula 1 and acrosslinkable compound. The catalyst layer includes a catalyst. Thepolymer of the naphthoxazine benzoxazine-based monomer represented byFormula 1 may be used as a binder of the electrode, and in particular,can act as a binder. Thus, a commonly used binder is not necessary forthe electrode.

The polymer of the naphthoxazine benzoxazine-based monomer of Formula 1is a material that improves wettability of phosphoric acid. The amountof the polymer may be in the range of 0.1 to 65 parts by weight based on100 parts by weight of the catalyst. When the amount of the polymer ofthe naphthoxazine benzoxazine-based monomer of Formula 1 is less than0.1 parts by weight based on 100 parts by weight of the catalyst,wettability of phosphoric acid in an electrode may be insufficientlyimproved. On the other hand, when the amount of the polymer of thenaphthoxazine benzoxazine-based monomer of Formula 1 is greater than 65parts by weight based on 100 parts by weight of the catalyst, membraneforming properties may be decreased.

The catalyst may be platinum alone, or an alloy or mixture of platinumand at least one metal selected from the group consisting of gold,palladium, rhodium, iridium, ruthenium, tin, molybdenum, cobalt, andchrome. Alternatively, the catalyst may be a support catalyst in whichthe catalyst metal is loaded on a carbonaceous support. In particular,the catalyst may be a catalyst metal including at least one of Pt, PtCo,and PtRu, or a support catalyst in which the catalyst metal is loaded ona carbonaceous support.

The electrode may further include a binder that can be conventionallyused in the preparation of an electrode for a fuel cell.

As non-limiting examples, the binder may be at least one selected fromthe group consisting of poly(vinylidenefluoride),polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylenecopolymer, and perfluoroethylene. The amount of the binder may be in therange of 0.1 to 50 parts by weight based on 100 parts by weight of thecatalyst. When the amount of the binder is less than 0.1 parts by weightbased on 100 parts by weight of the catalyst, the adhesion betweenelectrodes may be so poor that it may be difficult to maintain the shapeof a catalyst layer. On the other hand, when the amount of the binder isgreater than 50 parts by weight based on 100 parts by weight of thecatalyst, an electric resistance in the electrode may be increased.

The type and amount of the crosslinkable compound may be the same asdescribed above.

A method of preparing the electrode for a fuel cell described above isas follows.

First, a catalyst is dispersed in a solvent to obtain a dispersion. Thesolvent used may be N-methylpyrrolidone (NMP), dimethylformamide (DMAc),or the like, and the amount of the solvent may be in the range of 100 to1,000 parts by weight based on 100 parts by weight of the catalyst.

A mixture of the naphthoxazine benzoxazine-based monomer of Formula 1and a solvent is added to the dispersion and mixed together, and thenthe resultant is stirred. The mixture may further include a binder and acrosslinkable compound. The solvent may be N-methylpyrrolidone (NMP),dimethylacetamide (DMAc), or the like.

The resultant is coated on the surface of a carbon support to prepare anelectrode. The carbon support may be fixed on a glass substrate in orderto easily coat the resultant thereon. The coating method is notparticularly limited, but, may be coating using a doctor blade, barcoating, screen printing, or the like.

The coated resultant is dried at a temperature in the range of 20 to150° C., to remove the solvent. The drying time is dependent on thedrying temperature, and may be in the range of 10 to 60 minutes.

As can be seen in the method of preparing an electrode described above,the electrode for a fuel cell contains a polymer of the naphthoxazinebenzoxazine-based monomer of Formula 1. The naphthoxazinebenzoxazine-based monomer of Formula 1 is polymerized during the dryingprocess described above and/or while a fuel cell including the electrodeoperates.

If a crosslinking agent is further added to the mixture of thenaphthoxazine benzoxazine-based monomer, the solvent, and the binder,the prepared electrode includes a polymer of the benzoxazine-basedmonomer and the crosslinking agent.

Hereinafter, an electrolyte membrane and a method of preparing theelectrolyte membrane according to an embodiment of the present inventionwill be described. An electrolyte membrane formed using a crosslinkablecompound is described herein. However, when an electrolyte membrane isprepared only using the naphthoxazine benzoxazine-based monomer ofFormula 1, the preparation process is the same as that described herein,except that the crosslinkable compound is not used.

As a first method, the naphthoxazine benzoxazine-based monomerrepresented by Formula 1 may be blended with a crosslinkable compound,and the mixture is cured at a temperature in the range of 50 to 250° C.,or more specifically, 80 to 220° C. The cured mixture is impregnatedwith a proton conductor such as an acid to prepare an electrolytemembrane.

The cross-linkable compound may be at least one selected frompolybenzimidazoles (PBI), polybenzimidazole-base complexes,polybenzthiazoles, polybenzoxazoles, and polyimides. For example,polybenzimidazole-base complexes are disclosed in Korean Patent No.2007-102579.

The amount of the crosslinkable compound may be in the range of 5 to 95parts by weight based on 100 parts by weight of the naphthoxazinebenzoxazine-based monomer of Formula 1. When the amount of thecrosslinkable compound is less than 5 parts by weight, phosphoric acidmay not be sufficiently impregnated. On the other hand, when the amountof the crosslinkable compound is greater than 95 parts by weight, thecrosslinked object may be partially dissolved in a polyphosphoric acidin the presence of an excessive amount of phosphoric acid.

As a second method, an electrolyte membrane may be formed using amixture of the naphthoxazine benzoxazine-based monomer represented byFormula 1 and a crosslinkable compound.

The formation of the electrolyte membrane may be performed by a tapecasting method, or a conventional coating method. The conventionalcoating method may be a method in which the mixture is cast onto asupport using a doctor blade. Herein, a doctor blade with a 250 to 500μm gap may be used.

When the casting method using a doctor blade is used, the process offorming the electrolyte membrane further includes separating theelectrolyte membrane from the support, between the time when curing ofthe mixture occurs and the time when impregnation of the resultant withacid occurs. To separate the electrolyte membrane from the support, themixture is immersed in distilled water at temperature range of 60 to 80°C.

The support can be any support that can support an electrolyte membrane,such as, for example, a glass substrate, a polyimide film, and the like.When the tape casting method is used, a tape cast membrane is separatedfrom a support such as polyethyleneterephthalate before being cured, andthen put into an oven.

In addition, when a membrane is formed by the tape casting method usinga mixture of a benzoxazine-based monomer and polybenzimidazole, aprocess of filtering the mixture may be further performed.

The tape cast membrane is cured by heat treatment, and then isimpregnated with a proton conductor such as acid to form an electrolytemembrane.

Non-restrictive examples of the proton conductor include a phosphoricacid, and a C₁-C₂₀ organic phosphonic acid. As non-limiting examples,the C₁-C₂₀ organic phosphonic acid may be methyl phosphonic acid orethyl phosphonic acid.

The amount of the proton conductor may be in the range of 300 to 1,000parts by weight based on 100 parts by weight of the total weight of theelectrolyte membrane. The concentration of the acid used is notparticularly limited. As a non-limiting example, if phosphoric acid isused as the proton conductor, a 85 wt % aqueous phosphoric acid solutionmay be used, and the impregnation time of the phosphoric acid may be inthe range of 2.5 to 14 hours at 80° C.

A method of preparing a fuel cell using the electrode for a fuel cellaccording to an embodiment of the present invention will now bedescribed.

Any electrolyte membrane that is commonly used in the preparation offuel cells can be used herein. For example, the electrolyte membranethat is commonly used in a fuel cell may be a polybenzimidazoleelectrolyte membrane, a polybenzoxazine-polybenzimidazole copolymerelectrolyte membrane, a PTFE porous membrane, or the like.

Alternatively, an electrolyte membrane including a crosslinked productprepared by polymerization of the naphthoxazine benzoxazine-basedmonomer represented by Formula 1 and a crosslinkable compound may beused.

In particular, performance of the fuel cell including the electrode asdescribed herein may be maximized by using the electrolyte membraneincluding the polymer that is a crosslinked product prepared bypolymerization of the naphthoxazine benzoxazine-based monomerrepresented by Formula 1 and a crosslinkable compound.

A method of preparing a membrane-electrode assembly for a fuel cell,according to aspects of the present invention, is as follows. The term“membrane and electrode assembly (MEA)” used herein refers to astructure in which electrodes, each comprising a catalyst layer and adiffusion layer, are deposited on respective surfaces of the electrolytemembrane.

The MEA may be formed by positioning the electrodes each including thecatalyst layer for an electrode described above at respective sides ofthe electrolyte membrane, joining the electrolyte membrane andelectrodes together at a high temperature and a high pressure, and thenjoining a fuel diffusion layer to the catalyst layers.

Herein, the joining is performed under a pressure in the range of 0.1 to3 ton/cm², or more specifically, at a pressure of about 1 ton/cm², in astate reached when the MEA is heated up to a temperature that softensthe electrolyte membrane.

Next, a bipolar plate is disposed on each side of the membrane-electrodeassembly to prepare a fuel cell. The bipolar plate has grooves used forsupplying fuel, and functions as a current collector.

The use of the fuel cell according to aspects of the present inventionis not particularly limited. For example, the fuel cell may be used as apolymer electrolyte membrane (PEM) fuel cell.

Hereinafter, aspects of the present invention will be described morespecifically with reference to the following examples. The followingexamples are only for illustrative purposes and are not intended tolimit the scope of the invention.

SYNTHESIS EXAMPLE 1 Preparation of 16DHN-3AP represented by Formula 6

3.0 g of 1,6-dihydroxynaphthalene (18.7 mmol), 2.6 g ofpara-formaldehyde (82.4 mmol), and 3.88 g of 3-aminopyridine (41.2 mmol)were sequentially added to a 100 ml one-neck round bottomed flask, andthen mixed in an oil bath at 90° C.

The reaction mixture was transparent in an early stage of the reaction,and about 30 minutes after the reaction, the reaction mixture wasconverted into a dark brown material in the form of a transparent gel.The reaction mixture was quenched with tetrahydrofurane (THF) to becooled to room temperature. The crude product cooled to room temperaturewas base washed twice by solvent extraction using an aqueous 1N NaOHsolution, and then washed once again with deionized water.

After the washing process was terminated, an organic layer was driedusing MgSO₄, and then continuously filtered. The filtered solution wasremoved using a rotary evaporator, and then the purified product wasdried in a vacuum oven at 40° C. for 6 hours to obtain the targetmaterial.

FIG. 4 shows the nuclear magnetic resonance (NMR) spectrum of the targetmaterial prepared in Synthesis Example 1. The structure of the targetmaterial was confirmed by its NMR spectrum as shown in FIG. 4.

SYNTHESIS EXAMPLE 2 Preparation of 27DHN-34DFA represented by Formula 7

A target material was prepared in the same manner as in SynthesisExample 1, except that 14.41 g of 2,7-dihydroxynaphthalene (0.09 mmol),12.33 g of para-formaldehyde (0.39 mmol), and 25 g of3,4-difluoroaniline (0.194 mmol) were added to a 100 ml one-neck roundbottom flask instead of the materials described in Synthesis Example 1.

FIG. 5 shows the NMR spectrum of the target material prepared inSynthesis Example 2. The structure of the target material was confirmedby its NMR spectrum as shown in FIG. 5.

SYNTHESIS EXAMPLE 3 Preparation of 27DHN-2AP represented by Formula 8

A target material was prepared in the same manner as in SynthesisExample 1, except that 3.0 g of 2,7-dihydroxynaphthalene (18.7 mmol),2.6 g of para-formaldehyde (82.4 mmol), and 3.88 g of 2-aminopyridine(41.2 mmol) were added to a 100 ml one-neck round bottom flask insteadof the materials described in Synthesis Example 1.

FIG. 6 shows the NMR spectrum of the target material prepared inSynthesis Example 3. The structure of the target material was confirmedby its NMR spectrum as shown in FIG. 6.

SYNTHESIS EXAMPLE 4 Preparation of 16DHN246TFA represented by Formula 9

A target material was prepared in the same manner as in SynthesisExample 1, except that 6.06 g of 2,4,6-trifluoroaniline (41.2 mmol) wasused instead of 3.88 g of 3-aminopyridine (41.2 mmol).

FIG. 7 shows the NMR spectrum of the target material prepared inSynthesis Example 4. The structure of the target material was confirmedby its NMR spectrum as shown in FIG. 7.

SYNTHESIS EXAMPLE 5 Preparation of 15DHN3AP represented by Formula 10

A target material was prepared in the same manner as in SynthesisExample 1, except that 3.0 g of 1,5-dihydroxynaphthalene (18.7 mmol),2.6 g of para-formaldehyde (82.4 mmol), and 3.88 g of 3-aminopyridine(41.2 mmol) were added to a 100 ml one-neck round bottom flask insteadof the materials described in Synthesis Example 1.

The structure of the target material was confirmed by the nuclearmagnetic resonance (NMR) spectrum illustrated in FIG. 8.

SYNTHESIS EXAMPLE 6 Preparation of 27DHN246TFA represented by Formula 11

A target material was prepared in the same manner as in SynthesisExample 1, except that 3.0 g of 2,7-dihydroxynaphthalene (18.7 mmol),2.6 g of para-formaldehyde (82.4 mmol), and 6.06 g of2,4,6-trifluoroaniline (41.2 mmol) were added to a 100 ml one-neck roundbottom flask.

The structure of the target material was confirmed by the NMR spectrumillustrated in FIG. 9.

REFERENCE EXAMPLE 1 Preparation of t-BuPh-a

15 g of t-butylphenol (0.1 mol), 6.31 g of para-formaldehyde (0.21 mol),and 10.24 g of aniline (0.11 mol) were sequentially added in a 100 mlone-neck round bottom flask, and then mixed in an oil bath at 90° C.

The reaction mixture was opaque in an early stage of the reaction, andabout 30 minutes after the reaction, the reaction mixture was convertedinto a dark brown material in the form of a transparent gel. Thereaction mixture was quenched with tetrahydrofurane (THF) to be cooledto room temperature.

The crude product cooled to room temperature was base washed twice bysolvent extraction using an aqueous 1N NaOH solution, and then washedonce again with deionized water. After the washing process wasterminated, an organic layer was dried using MgSO₄, and thencontinuously filtered. The solvent was removed from the filteredsolution using a rotary evaporator, and then the purified product wasdried in a vacuum oven at 40° C. for 6 hours to obtain t-BuPh-a.

The structure of t-BuPh-a was confirmed by its NMR spectrum.

Thermal stabilities of the compound of Synthesis Example 1, the compoundof Synthesis Example 4, and t-BuPh-a of Reference Example 1 wereevaluated using thermogravimetric analysis (TGA). FIG. 1 is a graphshowing thermogravimetric analysis (TGA) results of the compoundprepared in Synthesis Example 1, the compound prepared in SynthesisExample 4, and t-BuPh-a prepared in Reference Example 1. In FIG. 1,thermogravimetric loss was measured at 800° C.

Referring to FIG. 1, it was confirmed that the compound of Formula 6 ofSynthesis Example 1 and the compound of Formula 9 of Synthesis Example 4had less thermogravimetric loss at a temperature of 800° C. or more thandid t-BuPh-a. From the result, it can be seen that the compound ofFormula 6 and the compound of Formula 9 have excellent thermal stabilitycompared to t-BuPh-a.

SYNTHESIS EXAMPLE 7 Preparation of polymer of 16DHN3AP and PBI

65 parts by weight of 16DHN3AP and 35 parts by weight ofpolybenzimidazole (PBI) were blended together, and the mixture was curedat a temperature in the range of about 180-240° C. to obtain a polymerof 16DHN3AP and PBI.

SYNTHESIS EXAMPLE 8 Preparation of polymer of 27DHN34DFA and PBI

65 parts by weight of 27DHN34DFA and 35 parts by weight ofpolybenzimidazole (PBI) were blended together, and the mixture was curedat a temperature in the range of about 180-240° C. to obtain a polymerof 27DHN34DFA and PBI.

Thermal stabilities of 16DHN3AP, 27DHN34DFA, and the polymer of 16DHN3APand PBI and the polymer of 27DHN34DFA and PBI that were prepared inSynthesis Examples 7 and 8, were evaluated using thermogravimetricanalysis (TGA). The results are respectively shown in FIGS. 10 and 11.In FIGS. 10 and 11, thermogravimetric loss was measured at 800° C.

Referring to FIGS. 10 and 11, it can be seen that 16DHN3AP, 27DHN34DFA,and the polymer of 16DHN3AP and PBI and the polymer of 27DHN34DFA andPBI that were prepared in Synthesis Examples 7 and 8 have excellentthermal stability.

The structure of the solid-phase polymer of 27DHN34DFA and PBI wasidentified by its solid nuclear magnetic resonance (NMR) spectrum asshown in FIG. 16. The NMR spectroscopy was performed using a VarianUnity INOVA600 at 600 MHz.

EXAMPLE 1 Preparation of electrode for fuel cell and fuel cell includingthe electrode

1 g of a catalyst in which 50 wt % of PtCo was supported on carbon and 3g of NMP were added in a stirrer, and the mixture was stirred using amortar to prepare a slurry. An NMP solution of 27DHN-34DFA of Formula 7of Synthesis Example 2 was added to the slurry so that the resultantcontained 0.025 g of 27DHN-34DFA. The resultant was further stirred.

Subsequently, an NMP solution of 5 wt % of polyvinylidenefluoride wasadded to the resultant so that the resultant contained 0.025 g ofpolyvinylidenefluoride. The resultant was mixed for 10 minutes toprepare a slurry used to form a cathode catalyst layer.

Carbon paper was cut to a size of 4×7 cm², fixed on a glass plate, andcoated by a doctor blade (Sheen instrument). The gap interval wasadjusted to 600 μm.

The slurry used to form a cathode catalyst layer was coated onto thecarbon paper, and the resultant was dried at room temperature for 1hour, dried at 80° C. for 1 hour, dried at 120° C. for 30 minutes, anddried at 150° C. for 15 minutes to prepare a cathode (a fuel electrode).The loading amount of PtCo in the prepared cathode was 2.1 mg/cm².

An electrode prepared by the following processes was used as an anode.

2 g of a catalyst in which 50 wt % of Pt was supported on carbon and 9 gof NMP were added to a stirrer, and the mixture was stirred for 2minutes using a high speed stirrer.

Subsequently, a solution in which 0.05 g of polyvinylidenefluoride wasdissolved in 1 g of NMP was added to the mixture, and the resultant wasfurther stirred for 2 minutes to prepare a slurry used to form an anodecatalyst layer. The slurry used to form an anode catalyst layer wascoated onto carbon paper coated with a microporous layer using a barcoater. As a result, preparation of the anode was completed. The loadingamount of Pt in the prepared anode was 1.3 mg/cm².

Separately, 60 parts by weight of a benzoxazine-based monomerrepresented by Formula 12 below, 3 parts by weight of abenzoxazine-based monomer represented by Formula 13 below, and 37 partsby weight of polybenzimidazole were blended together, and then themixture was cured at about 220° C.

Subsequently, the resultant was impregnated with 85 wt % of phosphoricacid at 80° C. for over 4 hours to form an electrolyte membrane. Theamount of phosphoric acid was about 480 parts by weight based on 100parts by weight of the total weight of the electrolyte membrane.

The electrolyte membrane was disposed between the cathode and the anodeto prepare a MEA. The cathode and anode were not impregnated withphosphoric acid.

To prevent gas permeation between the cathode and the anode, a TEFLONmembrane for a main gasket with a thickness of 200 μm and a TEFLONmembrane for a subgasket with a thickness of 20 μm were joined anddisposed between the electrode and the electrolyte membrane. Thepressure applied to the MEA was adjusted to 1, 2, 3 N-m torque step bystep using a wrench to assemble a cell.

Electricity was generated by causing hydrogen to flow into the anode(flowrate: 100 ccm) and causing air to flow into the cathode (flowrate:250 ccm) at 150° C. under a condition in which the electrolyte membranewas not humidified. Properties of the fuel cell prepared were measured.An electrolyte doped with a phosphoric acid was used, and thus theperformance of the fuel cell improved as time elapsed. Aging wasperformed until an operating voltage reached a peak, and then theproperties of the fuel cell were finally evaluated. In addition, thearea of the cathode and anode was fixed to a size of 2.8×2.8 (7.84 cm²),and the thickness of the cathode was about 430 μm and the thickness ofthe anode was about 390 μm, although the thicknesses of the cathode andthe anode may have varied according to the distribution of the carbonpaper.

EXAMPLE 2 Preparation of Electrode for Fuel Cell and Fuel Cell Includingthe Electrode

A cathode was prepared in the same manner as in Example 1, except that16DHN-3AP of Formula 6 of Synthesis Example 1 was used instead of27DHN-34DFA of Formula 7 of Synthesis Example 2, and a fuel cell usingthe cathode was prepared.

EXAMPLES 3-5 Preparation of Electrode for Fuel Cell and Fuel CellIncluding the Electrode

Cathodes were prepared in the same manner as in Example 1, except that27DHN-2AP of Formula 8 of Synthesis Example 3, 16DHN246TFA of Formula 9of Synthesis Example 4, and 15DHN3AP of Formula 10 of Synthesis Example5, respectively were used instead of 27DHN-34DFA of Formula 7 ofSynthesis Example 2, and fuel cells using the cathodes were prepared.

COMPARATIVE EXAMPLE 1 Preparation of Electrode for Fuel Cell and FuelCell Including the Electrode

A cathode was prepared in the same manner as in Example 1, except that27DHN-34DFA of Formula 7 of Synthesis Example 2 was not used, and a fuelcell using the cathode was prepared.

FIG. 2 is a graph showing a change in voltage with respect to time offuel cells prepared in Example 1 and Comparative Example 1.

Referring to FIG. 2, although the fuel cell of Example 1 had low initialperformance, it had improved voltage performance by faster activationcompared to the fuel cell of Comparative Example 1.

In addition, changes in cell potential with respect to current densityof the fuel cells of Examples 1 and 2 and Comparative Example 1 weremeasured, and the results are shown in FIG. 3.

Referring to FIG. 3, the fuel cells of Examples 1 and 2 had higher cellvoltage characteristics compared to the fuel cell of Comparative Example1.

Cell performances of the fuel cells of Examples 1 through 5 andComparative Example 1 were measured, and the results are shown in Table1 below.

TABLE 1 Voltage at Tafel slope 0.3 A/cm² (V) (mV/dec) 27DHN-34DFA(Example 1) 0.685 98 16DHN-3AP (Example 2) 0.685 99 27DHN-2AP (Example3) 0.686 104 16DHN246TFA (Example 4) 0.688 104 15DHN3AP (Example 5)0.684 108 Comparative Example 1 0.678 97 Referring to Table 1, the fuelcells of Examples 1 through 5 have a higher Tafel slope and improvedvoltage characteristics compared to the fuel cell of Comparative Example1.

EXAMPLE 6 Preparation of an Electrolyte Membrane for a Fuel Cell and aFuel Cell Using the Electrolyte Membrane

1 g of a catalyst in which 50% by weight of PtCo was loaded on carbonand 3 g of NMP as a solvent were added to a stirrer, and the mixture wasagitated using a mortar to prepare a slurry.

Then, a solution of 5% by weight of polyvinylidenefluoride and NMP wasadded to the mixture to set the amount of the polyvinylidenefluoride to0.025 g, and the mixture was mixed for 10 minutes to prepare a slurryfor a cathode catalyst layer.

Carbon paper was cut into pieces of 4×7 cm² in size, and the pieces werefixed on a glass plate and coated using a doctor blade (Sheeninstrument), wherein the gap interval of the doctor blade was 600 μm.

The slurry for a cathode catalyst layer was coated onto the carbon paperand dried at room temperature for 1 hour, at 80° C. for 1 hour, at 120°C. for 30 minutes and at 150° C. for 15 minutes to prepare a cathode (afuel electrode). The amount of loaded Pt/Co in the prepared cathode was2.32 mg/cm².

An electrode prepared according to the process as follows was used as ananode.

2 g of a catalyst in which 50% by weight of Pt is supported on carbonand 9 g of NMP solvent were added to a stirrer and the mixture wasagitated in a high-speed agitator for 2 minutes.

Then, a solution of 0.05 g of polyvinylidenefluoride dissolved in 1 g ofNMP was added thereto and agitated for 2 minutes to prepare a slurry foran anode catalyst layer. The slurry was coated onto carbon paper onwhich microporous layer was coated using a bar coater. The amount ofloaded Pt in the prepared anode was 1.44 mg/cm².

Separately, 65 parts by weight of 27DHN-34DFA of Formula 7 prepared inSynthesis Example 2 was blended with 35 parts by weight ofpolybenzimidazole (PBI), and the mixture was cured at about 220° C.

Then, the resultant was impregnated with 85% by weight of phosphoricacid at 80° C. for more than 4 hours to prepare an electrolyte membrane.The amount of phosphoric acid was about 530 parts by weight based on 100parts by weight of electrolyte membrane.

A membrane electrode assembly (MEA) was prepared by interposing theelectrolyte membrane between the cathode and the anode. The cathode andanode were not impregnated with phosphoric acid.

A 200 μm TEFLON membrane for a main gasket and a 20 μm TEFLON membranefor a sub gasket were overlapped on an interface between the electrodesand electrolyte membrane in order to prevent gas permeation between thecathode and the anode. The pressure applied to the MEA was adjusted to1, 2, 3 N-m torque step by step using a wrench to assemble a cell.

Characteristics of fuel cells were measured while operating by supplyinghydrogen to the anode at 100 ccm and supplying air to the cathode at 250ccm at 150° C. while the electrolyte membrane was not hydrated. Sincecell efficiency increases with time by using the electrolyte doped withphosphoric acid, the final efficiency was measured after the fuel cellwas aged until operational voltage was maximized. The area of thecathode and the anode was fixed to 2.8×2.8=7.84 cm², and the thicknessof the cathode was about 430 μm and the thickness of the anode was about390 μm although the thicknesses of the cathode and the anode may havevaried according to the distribution of the carbon paper.

EXAMPLES 7 TO 9 Preparation of an Electrolyte Membrane for a Fuel Celland a Fuel Cell Using the Electrolyte Membrane

An electrolyte membrane and a fuel cell were prepared in the same manneras in Example 6, except that 27DHN-246DFA, 16DHN-34DFA, and 16DHN-3APwere respectively used instead of 27DHN-34DFA of Formula 7 prepared inSynthesis Example 2.

Voltage characteristics according to current density of the fuel cellprepared in Example 6 were measured, and the results are shown in FIG.12. In FIG. 12, “OCV” denotes an open circuit voltage, and “0.2 A/cm²”denotes cell voltage at a current density of 0.2 A/cm².

Referring to FIG. 12, the fuel cell of Example 6 had an open circuitvoltage of more than 1 V and 0.72 V at 0.2 A/cm².

In addition, a change in cell voltage according to time was measured,and the results are shown in FIG. 13.

Referring to FIG. 13, the fuel cell of Example 6 showed excellent cellvoltage characteristics.

Conductivity according to temperature and phosphoric acid doping levelof the electrolyte membranes prepared in Examples 6 through 9 wasmeasured, and the results are shown in FIGS. 14 and 15.

Referring to FIGS. 14 and 15, the electrolyte membranes of Examples 6through 9 showed higher conductivity compared with the PBI electrolytemembrane, and showed good durability due to a small doping amount ofphosphoric acid.

In FIG. 15, the doping level is shown as a percentage based on theweight of the impregnated amount.

EXAMPLE 10 Preparation of a Fuel Cell

A fuel cell was prepared in the same manner as in Example 6, except thatthe slurry for a cathode catalyst layer was prepared in the followingprocesses.

1 g of a catalyst in which 50% by weight of PtCo was loaded on carbonand 3 g of NMP as a solvent were added to a stirrer, and the mixture wasagitated using a mortar to prepare a slurry. An NMP solution of27DHN-34DFA of Formula 7 prepared in Synthesis Example 2 was then addedto the slurry so that the resultant contained 0.025 g of 27DHN-34DFA.The resultant was further stirred.

Then, a solution of 5% by weight of polyvinylidenefluoride and NMP wasadded to the mixture to set the amount of the polyvinylidenefluoride to0.025 g, and the mixture was mixed for 10 minutes to prepare a slurryfor a cathode catalyst layer.

COMPARATIVE EXAMPLE 2 Preparation of Fuel Cell

A fuel cell was prepared in the same manner as in Example 10, exceptthat 27DHN-34DFA of Formula 7 was not used in the preparation of thecathode and a polybenzimidazole (PBI) membrane was used as anelectrolyte membrane.

Cell voltage characteristics with respect to current density of the fuelcells prepared in Example 10 and Comparative Example 2 were measured,and the results are shown in FIG. 17.

Referring to FIG. 17, performance of the MEA prepared in Example 10 wasimproved compared with that of the MEA prepared in Comparative Example2.

While aspects of the present invention have been particularly shown anddescribed with reference to differing embodiments thereof, it should beunderstood that these exemplary embodiments should be considered in adescriptive sense only and not for purposes of limitation. Descriptionsof features or aspects within each embodiment should typically beconsidered as available for other similar features or aspects in theremaining embodiments.

Although a few embodiments of the present invention have been shown anddescribed, it would be appreciated by those skilled in the art thatchanges may be made in this embodiment without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

What is claimed is:
 1. An electrolyte membrane for a fuel cell comprising a polymer that is a polymerization product of a naphthoxazine-based monomer or a polymerization product of the naphthoxazine-based monomer and a crosslinkable compound, wherein the naphthoxazine-based monomer is selected from compounds represented by Formulae 3 through 5 below:

and R₁ is one of the groups represented by the following formulae:


2. The electrolyte membrane of claim 1, further comprising at least one proton conductor selected from the group consisting of a phosphoric acid and a C₁-C₂₀ organic phosphonic acid.
 3. The electrolyte membrane of claim 1, wherein the crosslinkable compound is at least one compound selected from the group consisting of polybenzimidazole, a polybenzimidazole-base complex, polybenzthiazole, polybenzoxazole, and polyimide.
 4. An electrolyte membrane for a fuel cell comprising a polymer that is a polymerization product of the naphthoxazine-based monomer represented by Formulae 6-11 below or a polymerization product of the naphthoxazine-based monomer represented by Formulae 6-11 below and a crosslinkable compound:


5. The electrolyte membrane of claim 4, further comprising at least one proton conductor selected from the group consisting of a phosphoric acid and a C₁-C₂₀ organic phosphonic acid.
 6. The electrolyte membrane of claim 4, wherein the crosslinkable compound is at least one compound selected from the group consisting of polybenzimidazole, a polybenzimidazole-base complex, polybenzthiazole, polybenzoxazole, and polyimide.
 7. A fuel cell comprising: a cathode; an anode; and an electrolyte membrane interposed between the cathode and the anode, wherein: the electrolyte membrane is an electrolyte membrane comprising a polymer that is a polymerization product of a naphthoxazine-based monomer or a polymerization product of the naphthoxazine-based monomer and a crosslinkable compound, the naphthoxazine-based monomer is selected from compounds represented by Formulae 3 through 5 below:

and R₁ is one of the groups represented by the following formulae:


8. The fuel cell of claim 7, further comprising at least one proton conductor selected from the group consisting of a phosphoric acid and a C₁-C₂₀ organic phosphonic acid.
 9. The fuel cell of claim 7, wherein the crosslinkable compound is at least one compound selected from the group consisting of polybenzimidazole, a polybenzimidazole-base complex, polybenzthiazole, polybenzoxazole, and polyimide.
 10. A fuel cell comprising: a cathode; an anode; and an electrolyte membrane interposed between the cathode and the anode, wherein: the electrolyte membrane is an electrolyte membrane comprising a polymer that is a polymerization product of a naphthoxazine-based monomer or a polymerization product of the naphthoxazine-based monomer and a crosslinkable compound, and the naphthoxazine-based monomer is selected from compounds represented by Formulae 6 through 11 below: 